Process of coating iron or steel articles



No Drawing.

Patented July 13, 1926.

UNITED STATES 1,591,983 PATENT OFFICE.

.IRVIN J. KOEHNLINE, OF BRIDGEPORT, OHIO.

PROCESS OF COATING""I'RON...Q?B STEEL ARTICLES.

' all as will be more fully hereinafter disclosed and particularlypointed out inthe claims.

In order that the precise invention may be the more clearly understood,it is said In coating steel and iron sheets and shapes with tin alone bythe methods heretofore proposed of dipping the article in a bath ofmolten tin, the flux that is necessarily employed usually attacks themetal slightly,- and more or less hydrogen is produced. The action issuch that the hydrogen .does not completely escape from the metal beforethe sheet or shape is plunged below the surface of the molten tin, andit therefore often gives trouble at a later period. Again, uponimmersion in the molten tin, the sheet or shape becomes rapidly hotterthan it Was before, and any hydrogen or other gas adsorbed by the ironor steel, or present on the surface due to the action of the acid of theflux employed, is rapidly expanded, with the result that said gas forcesan exit through the tin coating, before it'is completely set. Thisescape of the expanded gases causes the formation of microscopicopenings or pits in the finished coating which frequently expose theiron or steel at the bottoms thereof. Later, when such tin coatedarticle is immersed in electrolytes, a galvanic couple between the ironand tin is formed'and the corrosion of the iron.becomes rapid.

I have found, however, that a small per centage of aluminum dissolved inthe molten tin bath effectually closes such pits by a precipitation ofthe aluminum onto the ex posed iron when such coated metal is immersedin an electrolyte as will be more fully explained below. .That is, thealuminum being electropositive to iron, under the conditions stated, acouple will be formed and the aluminum present will be deposited ontothe iron at the bottom of said pits, as will presently appear.-

Therefore, in carrying out this invention,

Application filed June 20,

1924. Serial No. 721,359.

I coat iron or steel sheets with an alloy of tin and aluminum in amanner similar to that heretofore employed in coating with tin .alone,but avoid the disadvantages stated,

and also accomplish the new results set forth below. a

The proportion of aluminum in the tinaluminum alloy forming the coatingis largely restricted by the temperature re-.

quired to maintain a sufficiently fluid melt for hot dipcoatings of thischaracter. Further, as is well known, articlesv coated by a dippingprocess are usually cooled by an immersion in palm oil, and it is foundif more than 10% aluminum is present in the tin-aluminum alloy coating,the tempera ture of the molten bath and of the dipped article will be sohigh that the palm oil bath will have to be relatively deep ifone is toprevent the palm oil from catching fire at the surface. Therefore, llprefer to use 1Q% of aluminum or less in the alloy, in order to enablethe use of a comparatively shallow cooling bath of oil to receive thetinned iron or steel as it emerges from the molten alloy bath, for thereis an advantage in employing shallow baths by means of which the coatedsheet or shape is to be sufiiciently.

cooled, when it reaches the air that oxidation will be either nothing orvery slight.

A tin-aluminum alloy containing from 1% to 20% aluminum, has a lowerdensity than pure tin, which enables a greater thickness or coating fora given weight per square foot than is the case with plain or pure tincoatings. This greater thickness serves as an additional protectionagainst an unavoidable scratching in handling the articles. As thealuminum is less costly by vwei ht than is tin, my tin-aluminum alloy is550 industrially less costly than is plain tin coatings of equal weightper unit of area.

Further, tinned iron or steel subjected to corrosion results in theformation of oxidized tin compounds which are physiologicallyundesirable, particularly when tin vessels are used as food containers,as is the case in making tin cans, because said compounds are more orless poisonous. My alloy containing aluminum being electro positive toboth tin and iron it results that under conditions inducing corrosion,it forms compounds of aluminum which are commonly inert physiologically,or nonpoisonous. As all the aluminum must be corroded before the tin isattacked my alloy supplies a coating of vastly greater sanitaryqualities than plain tin coatings.

My tin-aluminum coating is found to be harder than P1118 tin and istherefore in less danger of. being scored through the coating to theiron by the necessities of industrial handling in forming cans, etc.,than is a pure tin coating. Such scorings in the case of plain or puretin coatings furthermore expose the iron or steel base to the action ofelectrolytes, and a tin iron contact thus produced induces rapidcorrosion, as

'above stated, While my alloy coating prevents such corrosions. Further,I have found that this'alloy coating gives a longer life to containersand other articles than is the case with plain tin coatings.

same to the coating operation; immersing said articles in a molten bathof tin containing less than 20% of aluminum; and cooling the articlesthus coated.

3. The process of coating iron and steel articles which consistsinsuitably cleaning said articles preparatory to subjecting the same tothe coating operation; immersing said articles in a molten bath of tincontaining less than 15% of aluminum; and cooling in oil the articlesthus coated.

4. The process of coating iron and steel articles which consists insuitably cleaning said articles preparatory to subjecting the same tothe coating operation; immersing said articles in a molten bath of tincontaining less than 10% of aluminum; and cooling in palm oil thearticles thus coated.

5. The herein described new article of manufacture the same consistingof an iron or steel article provided with a coating of tin alloyed withless than 20% of aluminum.

In testimony whereof I affix my signature.

IRVIN J. KOEHNLIN E.

